Method for manufacturing wiring board, and wiring board

ABSTRACT

Provided is a method for manufacturing a wiring board that forms a wiring layer having favorable adhesion without a resin resist pattern. A method prepares a substrate with seed-layer including: a underlayer on the surface of an insulating substrate; and a seed layer on the surface of the underlayer, the seed layer having a predetermined pattern and containing metal; presses a solid electrolyte membrane against the seed layer and the underlayer, and applies voltage between an anode and the underlayer to reduce metal ions in the membrane and form a metal layer on the surface of the seed layer; and removes an exposed region without the seed layer and the metal layer of the underlayer to form a wiring layer including the underlayer, the seed layer and the metal layer on the surface of the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese patent applicationJP 2019-168980 filed on Sep. 18, 2019, the entire content of which ishereby incorporated by reference into this application.

BACKGROUND Technical Field

The present disclosure relates to methods for manufacturing a wiringboard to form a wiring layer on the surface of a substrate, and wiringboards.

Description of Related Art

Conventionally known methods of manufacturing a wiring board includes asubtractive method, a semi-additive method, and a full-additive method.Among these manufacturing methods, a semi-additive method is mainly usedfor a high-density wiring board.

JP 2016-225524 A, for example, discloses the method for manufacturing awiring board by a semi-additive method. The method of JP 2016-225524 Astacks a dielectric layer, a seed layer, and a first plating layer inthis order on the surface of a base layer (substrate), and forms aresist pattern of resin having a predetermined shape on the surface ofthe first plating layer. Then, the method forms a second plating layeron an exposed portion of the first plating layer without the resistpattern, and removes the resist pattern. After that, the method removesthe first plating layer and the seed layer using the second platinglayer as the mask to form a conductive pattern including the seed layer,the first plating layer and the second plating layer.

SUMMARY

The method of manufacturing a wiring board described in JP 2016-225524 Ahas to form the resist pattern of resin having a predetermined thicknesson the surface of the first plating layer to form the second platinglayer. When there is no need of the resist pattern during themanufacturing of the wiring board, the resist pattern has to be removed.In this way this method has the problems that a lot of steps is requiredto form and remove the resist pattern and a lot of liquid waste isgenerated.

In JP 2016-225524 A, the second plating layer is formed only on thesurface (upper face) of the first plating layer. The contact areabetween the second plating layer and the first plating layer thereforeis small especially for minute wiring, and improved adhesion between thesecond plating layer and the first plating layer is required.

In view of this, the present disclosure provides a method formanufacturing a wiring board capable of forming a wiring layer havingfavorable adhesion and without a resin resist pattern, and such a wiringboard.

A method for manufacturing a wiring board according to the presentdisclosure manufactures a wiring board including an insulatingsubstrate, and a wiring layer with a predetermined wiring patterndisposed on the surface of the insulating substrate, and the methodincludes: preparing a substrate with seed-layer, the substrate withseed-layer including: an electrically conductive underlayer on thesurface of the insulating substrate; and a seed layer with apredetermined pattern corresponding to the wiring pattern on the surfaceof the underlayer, the seed layer containing metal; disposing a solidelectrolyte membrane between an anode and the seed layer as a cathode,pressing the solid electrolyte membrane against the seed layer and theunderlayer, and applying voltage between the anode and the underlayer toreduce metal ions contained in the solid electrolyte membrane and soform a metal layer on the surface of the seed layer; and removing anexposed region of the underlayer without the seed layer and the metallayer to form the wiring layer including the underlayer, the seed layerand the metal layer on the surface of the insulating substrate, and somanufacture the wiring board. During formation of the metal layer on thesurface of the seed layer, at least a region of the surface of theunderlayer, on which the seed layer is not formed, contains oxide.

The method for manufacturing a wiring board of the present disclosureforms a metal layer on a substrate with seed-layer including: anunderlayer on the surface of the insulating substrate; and a seed layeron the surface of the underlayer. To this end, the method presses thesolid electrolyte membrane against the seed layer and the underlayer,and applies voltage between the anode and the underlayer to reduce metalions contained in the solid electrolyte membrane and so form a metallayer on the surface of the seed layer. The surface of the underlayercontains oxide, and such a surface of the underlayer thereforepresumably has higher activation energy for the reduction reaction ofthe metal ions than the surface (laminated surface) and the side facesof the seed layer. The solid electrolyte membrane is pressed against theseed layer and the underlayer, so that the solid electrolyte membranecomes into close contact with the underlayer as well as the seed layer.Nevertheless the method can selectively form the metal layer only on thesurface of the seed layer. The method therefore forms the metal layer onthe surface of the seed layer without using a resin resist pattern. Theexposed region of the underlayer without the seed layer and the metallayer is then removed, and this forms the wiring layer having apredetermined wiring pattern on the surface of the insulating substrate.As stated above, the method forms the metal layer on the surface of theseed layer without using a resin resist pattern, and so the method doesnot need the formation and removal of a resist pattern. As a result, themethod does not require a lot of steps to manufacture the wiring boardand does not generate a large amount of liquid waste.

The method applies voltage between the anode and the underlayer whilepressing the solid electrolyte membrane against the seed layer and theunderlayer, and so forms the metal layer while deforming the solidelectrolyte membrane so as to follow the shapes of the seed layer andthe underlayer. As a result, the metal layer is formed on the surface ofthe seed layer as well as the side faces of the seed layer, so that themetal layer is formed to cover the laminated face that is the surface ofthe seed layer and the side faces of the seed layer. This improves theadhesion between the metal layer and the seed layer as compared with thecase of the formation of the metal layer only on the surface of the seedlayer.

In some embodiments of the method for manufacturing the wiring board asstated above, during formation of the metal layer on the surface of theseed layer, a natural oxide film including the oxide is formed in atleast a region of the surface of the underlayer, on which the seed layeris not formed. This configuration facilitates the formation of theunderlayer so that the underlayer contains oxide at the surface. Thenatural oxide film refers to an oxide film that is naturally formed onthe surface of a substance when the substance is left in the atmosphere.In one example, the natural oxide film includes a passive film formed onthe surface of Al, Cr, Ti and its alloys, and SiO₂ formed on the surfaceof ZrSi₂ and WSi₂.

In some embodiments of the method for manufacturing the wiring board asstated above, when copper sulfate solution with concentration of 1 mol/Lat a temperature of 25° C. is used as an electrolyte, oxygen-free copperwire is used as a counter electrode, a saturated calomel electrode isused as a reference electrode, and a first polarization curve using thematerial of the underlayer as a working electrode and a secondpolarization curve using the metal of the seed layer as a workingelectrode are measured while setting the potential sweep rate at 10mV/sec, potential of the first polarization curve at a current densityof 0.1 mA/cm² is higher than potential of the second polarization curveat a current density of 0.1 mA/cm² by 0.02 V or more. This configurationenables a sufficiently large difference (about 0.02 V or more) in risingpotential of the polarization curve between the material of theunderlayer and the material of the seed layer, and so allows selectiveformation of the metal layer only on the surface of the seed layer ofthe seed layer and the underlayer that are in close contact with thesolid electrolyte membrane during formation of the metal layer on thesurface of the seed layer.

In some embodiments of the method for manufacturing the wiring board asstated above, when preparing the substrate with seed-layer, the methodprepares a substrate including a surface with center-line averageroughness Ra of 1 μm or less as the insulating substrate, and forms theunderlayer by sputtering on the surface of the insulating substrate.Typically the contact area between the substrate and the underlayerdecreases with the center-line average roughness Ra of the substrate,and so the adhesion decreases accordingly. Conventional methods ofmanufacturing a wiring board therefore roughens the surface of thesubstrate to obtain the adhesion between the substrate and theunderlayer from the anchor effect. As stated above the method of thepresent disclosure forms the underlayer on the surface of the insulatingsubstrate by sputtering to firmly bond the substrate and the underlayerdue to covalent bond. That is, even when the substrate has thecenter-line average roughness Ra of 1 μm or less, the methodsufficiently keeps the adhesion between the substrate and theunderlayer. The method therefore does not need roughening of the surfaceof the substrate to keep the adhesion between the substrate and theunderlayer.

In some embodiments, the seed layer is formed on the surface of theunderlayer so that line/space is 2 μm or more and 100 μm or less/2 μm ormore and 100 μm or less. Such center-line average roughness Ra of theinsulating substrate of 1 μm or less decreases the center-line averageroughness Ra of the underlayer as well. When ink is disposed on thesurface of the underlayer, such an underlayer suppresses the deformationof the ink due to the surface shape (surface irregularities) of theunderlayer. This leads to easy formation of the seed layer having a fineline/space of 2 μm or more and 100 μm or less/2 μm or more and 100 μm orless. Such a fine seed layer means very small contact area between themetal layer and the seed layer if the metal layer is formed only on thesurface of the seed layer, and this degrades the adhesion between themetal layer and the seed layer. In this respect, the method formanufacturing the wiring board of the present disclosure forms the metallayer so as to cover the surface and the side faces of the seed layer asdescribed above. This improves the adhesion between the metal layer andthe seed layer. In this way, the fine seed layer also easily keeps theadhesion between the metal layer and the seed layer.

In some embodiments of the method for manufacturing the wiring board asstated above, when preparing the substrate with seed-layer, the methodplaces ink containing metal nanoparticles on the surface of theunderlayer, and then sinters the metal nanoparticles to form the seedlayer. Such ink containing metallic nanoparticles enables easy formationof the seed layer having a fine pattern.

In some embodiments of the method for manufacturing the wiring board asstated above, when preparing the substrate with seed-layer, the methodforms the seed layer on the surface of the underlayer so that thepredetermined pattern of the seed layer has a plurality of independentpatterns that are spaced away from each other. Even in the configurationof the seed layer having a plurality of independent patterns spaced awayfrom each other, these independent patterns are electrically connectedto each other through the underlayer, and the metal layer is thereforeformed also on the independent patterns of the seed layer when voltageis applied between the anode and the underlayer. That is, whileconventional methods require the formation of a lead to apply voltage toeach of the plurality of independent patterns disposed apart from eachother, this manufacturing method does not require a lead to applyvoltage to each of the independent patterns, because the independentpatterns are electrically connected to each other through theunderlayer. In this way there is no need for a space for forming thelead, and so the method easily forms a higher density wiring pattern.

A wiring board according to the present disclosure includes aninsulating substrate, and a wiring layer with a predetermined wiringpattern disposed on the surface of the insulating substrate. The wiringlayer includes the lamination of: an electrically conductive underlayerdisposed on the surface of the insulating substrate; a seed layerdisposed on the surface of the underlayer and containing metal; and ametal layer disposed on the surface of the seed layer. The seed layerincludes a side face extending from a laminated surface that is thesurface of the seed layer toward the underlayer. The metal layer coversthe surface and the side face of the seed layer. At least a region ofthe surface of the underlayer, on which the seed layer is not formed,contains oxide.

According to the wiring board of the present disclosure, the metal layercovers the surface and the side face of the seed layer. This improvesthe adhesion between the metal layer and the seed layer as compared withthe case of the formation of the metal layer only on the surface of theseed layer.

The wiring board of the present disclosure can be manufactured by themethod for manufacturing a wiring board as stated above.

In some embodiments of the wiring board as stated above, the metal layeron the surface of the seed layer has a thickness that is larger than athickness of the metal layer on the side face. This configuration keepsthe thickness of the wiring layer without narrowing the wiring intervalof the wiring layer, and so easily keeps the insulation reliabilitybetween the wirings.

In some embodiments of the wiring board as stated above, the wiringlayer is formed in a taper shape that tapers in accordance with adistance from the insulating substrate in a portion closer to theinsulating substrate than the surface of the seed layer, and is formedin a reverse taper shape that becomes thicker in accordance with adistance from the insulating substrate in a portion farther from theinsulating substrate than the surface of the seed layer. The wiringlayer has a width of the taper-shaped part that is smaller than a widthof the reverse taper-shaped part. This configuration keeps the wiringwidth with the reverse taper-shaped part, and widens the wiring interval(wiring interval in the vicinity of the surface of the insulatingsubstrate) between the taper-shaped parts. The wiring board thereforekeeps insulation reliability between the wirings.

In some embodiments of the wiring board as stated above, the seed layerhas line/space of 2 μm or more and 100 μm or less/2 μm or more and 100μm or less. Such a fine seed layer means very small contact area betweenthe metal layer and the seed layer if the metal layer is formed only onthe surface of the seed layer, and this degrades the adhesion betweenthe metal layer and the seed layer. In this respect, the wiring board ofthe present disclosure includes the metal layer disposed to cover thesurface and the side face of the seed layer as described above. Thisconfiguration improves the adhesion between the metal layer and the seedlayer, and so easily keeps the adhesion between the metal layer and thefine seed layer.

Effect

The present disclosure provides a wiring board having a wiring layerwith favorable adhesion that is formed without a resin resist pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of the method for manufacturing a wiring boardaccording to one embodiment of the present disclosure;

FIG. 2 schematically shows the method for manufacturing a wiring boardaccording to one embodiment of the present disclosure;

FIG. 3 is a plan view of a seed layer formed to have independentpatterns on the surface of the underlayer of the wiring board that isone embodiment of the present disclosure;

FIG. 4 is a cross-sectional view showing the structure of afilm-deposition apparatus that is used to manufacture a wiring boardaccording to one embodiment of the present disclosure;

FIG. 5 is a cross-sectional view of the film-deposition apparatus whenthe housing is lowered to a predetermined height from the state of FIG.4;

FIG. 6 is a cross-sectional view showing a solid electrolyte membranethat is in close contact with the side faces of the seed layer;

FIG. 7 shows polarization curves (polarization characteristics) of WSi₂,ZrSi₂, ITO, Ti, WC, and Ag (silver);

FIG. 8 is a cross-sectional view showing the solid electrolyte membranethat is away from the side faces of the seed layer;

FIG. 9 is a cross-sectional view showing the structure of a wiring layerin a wiring board according to one embodiment of the present disclosure;

FIG. 10 shows photos from the above, showing the wiring layers inExamples 1 to 4 and Comparative Example 1;

FIG. 11 shows photos from the above, showing the wiring layers inExamples 1 and 6 to 11;

FIG. 12 shows the result of the peeling test for Examples 12 to 15 andComparative Examples 2 to 5; and

FIG. 13 shows photos from the above, showing the wiring layer in Example16.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following describes a wiring board and a method for manufacturingthe wiring board according to embodiments of the present disclosure.

Firstly the following describes a method for manufacturing a wiringboard 1 according to one embodiment of the present disclosure. FIG. 1 isa flowchart of the method for manufacturing the wiring board 1 accordingto one embodiment of the present disclosure. As shown in FIG. 1, themethod for manufacturing the wiring board 1 includes an underlayerformation step S1, a seed-layer formation step S2, a metal-layerformation step S3 and a removal step S4. The following describes anexample of the method for manufacturing the wiring board 1 of thepresent disclosure that includes the underlayer formation step S1 andthe seed-layer formation step S2. In another example, the method formanufacturing the wiring board 1 of the present disclosure does notinclude the underlayer formation step S1 and the seed-layer formationstep S2, and may include a step of preparing a substrate with seed-layer9 having an underlayer 4 on the surface of an insulating substrate 2 anda seed layer 5 on the surface of the underlayer 4. The method formanufacturing the wiring board 1 of the present disclosure does notinclude the underlayer formation step S1, and may include a step ofpreparing a substrate with underlayer having an underlayer 4 on thesurface of a substrate 2 and a seed-layer formation step S2. In anycase, the method can prepare the substrate with seed-layer 9 includingthe substrate 2, the underlayer 4 and the seed layer 5.

As shown in FIG. 2, the underlayer formation step S1 forms theunderlayer 4 having electrical conductivity on the surface of theprepared insulating substrate 2. The underlayer 4 is formed on theentire surface of the substrate 2 without using a mask.

The substrate 2 is not particularly limited, and in some embodiments,the substrate 2 is made of a glass epoxy resin, is a flexible film-likesubstrate made of polyimide resin, for example, or is a substrate madeof glass. Particularly in some embodiments, a substrate made of glassepoxy resin is used. When the substrate 2 is made of resin, examples ofthe resin include thermoplastic resin, such as ABS resin, AS resin, AASresin, PS resin, EVA resin, PMMA resin, PBT resin, PET resin, PPS resin,PA resin, POM resin, PC resin, PP resin, PE resin, polymer alloy resincontaining elastomer and PP, modified PPO resin, PTFE resin, or ETFEresin, thermosetting resin, such as phenol resin, melamine resin, aminoresin, unsaturated polyester resin, polyurethane, diallylphthalate,silicone resin or alkyd resin, resin obtained by adding cyanate resinto, for example, epoxy resin, and liquid crystal polymer.

In some embodiments, the surface of the substrate 2 (upper face in FIG.2) is a flat face. The center-line average roughness Ra of the surfaceof the substrate 2 is not particularly limited, and is 1 μm or less insome embodiments. Such center-line average roughness Ra of the substrate2 of 1 μm or less decreases the center-line average roughness Ra of theunderlayer 4 as well. When ink is disposed on the surface of theunderlayer 4 as described later, this suppresses the deformation of theink due to the surface shape (surface irregularities) of the underlayer4. This configuration leads to easy formation of the seed layer 5 havinga fine line/space of 2 μm or more and 100 μm or less/2 μm or more and100 μm or less, for example, as described later. In the presentspecification and claims, the center-line average roughness Ra is avalue measured according to JIS B0601-1994.

The underlayer 4 has oxide on the surface. Examples of the layer havingoxide on the surface include a layer on the surface of which a naturaloxide film is formed, and a layer containing oxide in the entire layer.In some embodiments, the underlayer 4 is a layer on the surface of whicha natural oxide film is formed. The natural oxide film refers to anoxide film that is naturally formed on the surface of a substance whenthe substance is left in the atmosphere. The natural oxide film includesa passive film formed on the surface of Al, Cr, Ti and its alloys, andSiO₂ formed on the surface of ZrSi₂ and WSi₂.

When the underlayer 4 is a layer on the surface of which a natural oxidefilm is formed, such an underlayer 4 may be made of silicide in someembodiments. Silicide refers to a compound composed of metal andsilicon. When the underlayer 4 is made of silicide, the silicide istransition metal silicide in some embodiments. Transition metal siliciderefers to silicide composed of transition metal and silicon. When theunderlayer 4 is made of transition metal silicide, example of thetransition metal silicide includes FeSi₂, CoSi₂, MoSi₂, WSi₂, VSi₂,ReSi_(1.75), CrSi₂, NbSi₂, TaSi₂, TiSi₂ or ZrSi₂ in some embodiments,and ZrSi₂ or WSi₂ in some embodiments.

The material of the underlayer 4 is not particularly limited, andexamples of the material include transition metal silicide, such asZrSi₂ or WSi₂, metal oxide, such as ITO (indium tin oxide), Ti, alloyscontaining Ti, alloys containing Cr, such as stainless steel, andconductive resin in some embodiments. Particularly the underlayer 4 ismade of transition metal silicide, such as ZrSi₂ or WSi₂ in someembodiments. The thickness of the underlayer 4 is not particularlylimited, and is 20 nm or more and 300 nm or less in some embodiments.The thickness of the underlayer 4 less than 20 nm may cause unevennessin part of the metal layer 6 at the metal-layer formation step S3described later. The thickness of the underlayer 4 more than 300 nmfavorably forms the metal layer 6 at the metal-layer formation step S3described later, but the material cost and the process cost required forforming and removing the underlayer 4 will increase, and so the costeffectiveness deteriorates.

In one example, the underlayer 4 may be formed by sputtering. This formscovalent bonding of the underlayer 4 and the substrate 2 and so allowstight bonding of the underlayer 4 with the substrate 2. Even when thesubstrate 2 has the center-line average roughness Ra of 1 μm or less,such an underlayer 4 suppresses peeling off of the underlayer 4 from thesubstrate 2. That is, even when the substrate 2 has the center-lineaverage roughness Ra of 1 μm or less, such an underlayer 4 keepssufficient adhesion between the substrate 2 and the underlayer 4. Whenthe substrate 2 is made of glass epoxy resin and the underlayer 4 ismade of transition metal silicide, such as WSi₂ or ZrSi₂, this easilyincreases the adhesion between the underlayer 4 and the substrate 2. Themethod for forming the underlayer 4 is not particularly limited, andanother method, such as deposition including PVD (physical vapordeposition) and CVD (chemical vapor deposition), or plating, may be usedinstead of the sputtering. Such tight bonding of the underlayer 4 andthe substrate 2 due to covalent bonding eliminates the necessity ofroughening of the surface of the substrate 2 to keep the adhesionbetween the underlayer 4 and the substrate 2. Typically the contact areabetween the substrate 2 and the underlayer 4 decreases with thecenter-line average roughness Ra of the substrate 2, and the adhesiondecreases accordingly. Conventional wiring boards therefore requireroughening of the surface of the substrate.

The seed-layer formation step S2 forms the seed layer 5 having apredetermined pattern and containing metal on the surface of theunderlayer 4. This forms the substrate with seed-layer 9 including thesubstrate 2, the underlayer 4 and the seed layer 5.

It is undesirable that the seed layer 5 is made of the same material asthat of the underlayer 4, because the metal layer 6 cannot beselectively formed on the surface of the seed layer 5 as describedlater. In some embodiments, the seed layer 5 is a layer on the surfaceof which a natural oxide film is not formed or a layer which does notcontain oxide in the entire layer. If a natural oxide film is formed onthe surface of the seed layer 5, the seed layer 5 has a smallerthickness of the natural oxide film than the natural oxide film of theunderlayer 4 in some embodiments. Specifically, examples of the materialof the seed layer 5 include silver, copper, gold, palladium, andplatinum, and particularly the seed layer 5 is made of silver or copperin some embodiments. The material of the seed layer 5 may be two or moretypes selected from the group consisting of silver, copper, gold,palladium and platinum.

The thickness of the seed layer 5 is not particularly limited, and thethickness is 20 nm or more and 300 nm or less in some embodiments. Thethickness of the seed layer 5 less than 20 nm may cause unevenness inpart of the metal layer 6 at the metal-layer formation step S3 describedlater. The thickness of the seed layer 5 more than 300 nm favorablyforms the metal layer 6 at the metal-layer formation step S3 describedlater, but the material cost and the process cost required for formingthe seed layer 5 will increase, and so the cost effectivenessdeteriorates. The line/space of the seed layer 5 is not particularlylimited, and is 2 μm or more and 100 μm or less/2 μm or more and 100 μmor less, for example. That is, in one example, the line (line width) W11of the seed layer 5 is 2 μm or more and 100 μm or less, and the space(line space) W12 in the seed layer 5 is 2 μm or more and 100 μm or less.The line/space is the line width W11/fine space W12 in a plan view ofthe wiring board 1. The line (line width) W11 and the space (line space)W12 of the seed layer 5 may be the same dimension or may be differentdimensions.

Such a fine seed layer 5 means very small contact area between the metallayer 6 and the seed layer 5 if the metal layer 6 is formed only on thesurface (laminated face) 5 a of the seed layer 5. This degrades theadhesion between the metal layer 6 and the seed layer 5. The wiringboard 1 of the present disclosure includes the metal layer 6 disposed tocover the surface 5 a and the side face 5 b of the seed layer 5 asdescribed later. This improves the adhesion between the metal layer 6and the seed layer 5, and so easily keeps the adhesion between the metallayer 6 and the fine seed layer 5.

As shown in FIG. 3, the seed layer 5 is formed to have a plurality ofindependent patterns 5 c that are disposed apart from each other. InFIG. 3, the plurality of independent patterns 5 c are hatched. Theplurality of independent patterns 5 c is electrically connected to eachother through the underlayer 4, and the metal layer 6 is thereforeformed also on the independent patterns 5 c of the seed layer 5 at themetal-layer formation step S3 described later. That is, whileconventional methods require the formation of a lead to apply voltage toeach of the plurality of independent patterns disposed apart from eachother, the manufacturing method of the present embodiment does notrequire the formation of a lead to apply voltage to each of theindependent patterns 5 c, because the independent patterns 5 c areelectrically connected to each other through the underlayer 4. In thisway there is no need for a space for forming the lead, and so the methodeasily forms a higher density wiring pattern.

In one example, the seed-layer formation step S2 disposes ink containingmetal particles on the surface of the underlayer 4 and solidifies theink to form the seed layer 5 having a predetermined pattern. The methodfor disposing the ink on the surface of the underlayer 4 is not limitedespecially, and various print methods, such as screen printing, inkjetprinting, and transfer printing, may be used. In one example, the seedlayer 5 may be formed without using ink and by evaporation orsputtering. The method for solidifying the disposed ink on the surfaceof the underlayer 4 is not limited especially, and various methods maybe used, such as sintering of metal particles in the ink or solidifyingthe ink by heating or drying. When the seed layer 5 is formed bysintering, the sintering is performed at the heatproof temperature ofthe substrate 2 or lower (for example, about 250° C. or lower when thesubstrate 2 is made of glass epoxy resin).

The material of the metal particles in the ink is not especiallylimited, and examples of the material include silver, copper, gold,palladium, and platinum in some embodiments. Particularly the metalparticles are made of silver or copper in some embodiments. The materialof the metal particles may be two or more types selected from the groupconsisting of silver, copper, gold, palladium and platinum. The particlediameter of the metal particles is not particularly limited, and theparticle diameter is smaller in some embodiments to form the wiring inthe μm order. In one example, the particle diameter is in the nm orderthat is 1 nm or more and 100 nm or less. Such metal particles are alsocalled metal nanoparticles. In one example, the metal nanoparticleshaving a particle diameter of 20 nm or less may be used, and this lowersthe melting point of the metal particles and so enables easy sintering.Ink containing metallic nanoparticles enables easy formation of the seedlayer 5 having a fine pattern.

The dispersion medium and additives contained in the ink are notparticularly limited, and they have a property of volatilizing duringsintering in some embodiments. In one example, decanol can be used asthe dispersion medium, and a linear fatty acid salt having about 10 to17 carbon atoms can be used as the additive.

In cross-sectional view, the seed layer 5 has the surface (upper surfacein FIG. 2) 5 a on the side opposite to the substrate 2 side and the sidefaces 5 b extending from both ends of surface 5 a toward the substrate2. In cross-sectional view, the seed layer 5 has a taper shape thattapers in accordance with a distance from the substrate 2 or has arectangular shape.

In the present embodiment, before the metal-layer formation step S3, thesurface 4 a of the underlayer 4 contains oxide. The oxide is notparticularly limited. The oxide may be a natural oxide film that isformed on the surface of silicide, such as ZrSi₂ or WSi₂, or on thesurface of metal, such as Ti or stainless steel. The oxide may be anoxide film separately disposed on the surface of silicide, metal or thelike as long as the seed layer 5 can be selectively energized. Oxideincluding a natural oxide film enables easy formation of the underlayer4, the surface 4 a of which contains oxide. In one example, when theunderlayer 4 includes silicide, such as ZrSi₂ or WSi₂, a natural oxidefilm including SiO₂ is formed on the surface of the silicide. When theoxide includes a natural oxide film, such a natural oxide film is formedon the entire surface 4 a of the underlayer 4. When the oxide includes aseparately disposed oxide film, such an oxide film is formed on the areain the surface 4 a of the underlayer 4 without the seed layer 5 afterthe seed-layer formation step S2. In any case, at least the area in thesurface 4 a of the underlayer 4 without the seed layer 5 contains oxide.

The metal-layer formation step S3 forms the metal layer 6 on the surface5 a of the seed layer 5. The material of the metal layer 6 is notespecially limited, and examples of the material include copper, nickel,silver and gold in some embodiments. Particularly the metal layer 6 ismade of copper in some embodiments. The thickness of the metal layer 6is not particularly limited, and the thickness is 1 μm or more and 100μm or less in some embodiments.

The following describes the structure of a film-deposition apparatus 100(see FIG. 4) used for forming the metal layer 6 at the metal-layerformation step S3. This film-deposition apparatus 100 is afilm-deposition apparatus (plating apparatus) used to deposit metalliccoating (the metal layer 6 in the present embodiment) by solidelectrodeposition, and forms the metal layer 6 on the surface 5 a of theseed layer 5.

As shown in FIG. 4, the film-deposition apparatus 100 includes a metalanode 11, a solid electrolyte membrane 13 disposed between the anode 11and a seed layer 5 that is a cathode, and a power supply 16 to applyvoltage between the anode 11 and the underlayer 4. The underlayer 4 andthe seed layer 5 are electrically connected, and therefore electriccurrent flows between the anode 11 and the seed layer 5 during filmdeposition by applying voltage between the anode 11 and the underlayer 4from the power supply 16.

In the present embodiment, the film-deposition apparatus 100 furtherincludes a housing 15. The housing 15 stores the anode 11 and solution L(hereinafter referred to as metallic solution L) containing metal ions,such as copper, nickel, silver or gold, that is the material of themetallic coating (the metal layer 6 in this case) to be formed. Morespecifically, a space for containing the metallic solution L is definedbetween the anode 11 and the solid electrolyte membrane 13, and themetallic solution L stored in the space flows from one side to the otherside.

The anode 11 has a plate shape, and may be either a soluble anode madeof the same material (e.g., copper) as the metallic coating (the metallayer 6 in this case) or an anode made of a material (e.g., titanium)that is insoluble in the metallic solution L. In the present embodiment,the anode 11 and the solid electrolyte membrane 13 are disposed awayfrom each other. In another embodiment, the anode 11 and the solidelectrolyte membrane 13 may come in contact with each other, and theanode 11 may include a porous body that transmits the metallic solutionL and supplies metal ions to the solid electrolyte membrane 13. In thiscase, when the anode 11 is pressed against the solid electrolytemembrane 13, uneven deposition may occur due to a variation in thepressing force of the anode 11 against the solid electrolyte membrane13. Such a configuration of pressing the anode 11 against the solidelectrolyte membrane 13 is therefore not favorable to manufacturing finewiring. However, when the wiring is not fine, the adverse effect fromuneven deposition is small, and therefore the housing 15 may have thestructure of pressing the anode 11 against the solid electrolytemembrane 13.

The solid electrolyte membrane 13 is not particularly limited, as longas when the solid electrolyte membrane 13 comes in contact with themetallic solution L as stated above, the solid electrolyte membrane 13can be impregnated with (contain) metal ions, and when voltage isapplied, the metal originating from the metal ions can be deposited onthe surface of the cathode (seed layer 5). In one example, the thicknessof the solid electrolyte membrane 13 is about 5 μm to about 200 μm.Examples of the material of the solid electrolyte membrane 13 includeresin having a cation exchange function, including fluorine-based resin,such as Nafion (registered trademark) manufactured by DuPont,hydrocarbon resin, polyamic acid resin, and Selemion (CMV, CMD, CMFseries) manufactured by Asahi Glass Co.

As stated above, the metallic solution L is liquid containing the metalof the metallic coating to be formed in an ionic state, and examples ofthe metal include copper, nickel, silver and gold. The metallic solutionL is a solution (ionization) of these metals with an acid, such asnitric acid, phosphoric acid, succinic acid, nickel sulfate, orpyrophosphoric acid.

The film-deposition apparatus 100 further includes an elevator 18 abovethe housing 15 to move the housing 15 up and down. The elevator 18 isnot particularly limited as long as it can move the housing 15 up anddown. In one example, the elevator 18 may include a hydraulic orpneumatic cylinder, an electric actuator, a linear guide, and a motor.The housing 15 has an inlet 15 a for receiving the supplied metallicsolution L and an outlet 15 b for discharging the metallic solution L.These inlet 15 a and outlet 15 b connect to a tank 101 via a pipe. Themetallic solution L sent from the tank 101 by the pump 102 flows intothe housing 15 through the inlet 15 a, is discharged from the outlet 15b, and returns to the tank 101. The film-deposition apparatus 100includes a pressure regulation valve 103 downstream of the outlet 15 b,and the pressure regulation valve 103 and the pump 102 pressurize themetallic solution L in the housing 15 with a predetermined pressure.With this configuration, the solid electrolyte membrane 13 presses theseed layer 5 due to the liquid pressure of the metallic solution Lduring film deposition. As a result, the metallic coating (the metallayer 6) can be formed on the seed layer 5 while uniformly pressing theseed layer 5 with the solid electrolyte membrane 13.

The film-deposition apparatus 100 of this embodiment includes a metallicmount 40 to mount the substrate 2. The metallic mount 40 electricallyconnects (is conductive) to the negative electrode of the power supply16. The positive electrode of the power supply 16 electrically connects(is conductive) to the anode 11 that is built in the housing 15.

Specifically, the film-deposition apparatus 100 includes a conductivemember 17 that comes in contact with a part of the underlayer 4 or theseed layer 5 (specifically with their ends) during film deposition ofthe metallic coating so as to establish electric continuity between thenegative electrode of the power supply 16 and the underlayer 4 or theseed layer 5. The conductive member 17 can be attached to the substrate2 so as to come into contact with a part of the underlayer 4 during filmdeposition, and can be detached from the substrate 2. The conductivemember 17 is a metal plate that covers a part of the edge of thesubstrate 2, and a part of the conductive member 17 is bent so as to bein contact with the metallic mount 40. This allows the metallic mount 40to be conductive to the underlayer 4 via the conductive member 17. Theconductive member 17 may be formed to come into contact with a part ofthe seed layer 5. In this case also, the part of the seed layer 5 thatis in contact with the conductive member 17 is conductive to the otherpart of the seed layer 5 via the underlayer 4.

As shown in FIG. 4, the metal-layer formation step S3 places thesubstrate 2 and the conductive member 17 at predetermined positions onthe metallic mount 40. Then, as shown in FIG. 5, the elevator 18 lowersthe housing 15 to a predetermined height. When the metallic solution Lis pressurized by the pump 102, the solid electrolyte membrane 13 isdeformed to follow the shapes of the seed layer 5 and the underlayer 4as shown in FIG. 6, and the metallic solution L in the housing 15 has aset constant pressure by the pressure regulation valve 103. That is, thesolid electrolyte membrane 13 is able to uniformly press the surface 5 aand the side faces 5 b of the seed layer 5 and the surface 4 a of theunderlayer 4 with the adjusted liquid pressure of the metallic solutionL in the housing 15. In this way, while the solid electrolyte membrane13 presses the surface 5 a and the side faces 5 b of the seed layer 5and the surface 4 a of the underlayer 4, voltage is applied between theanode 11 and the underlayer 4. As a result, metal originating from themetal ions contained in the solid electrolyte membrane 13 is depositedon the surface 5 a and the side faces 5 b of the seed layer 5. Thevoltage applied reduces metal ions in the metallic solution L in thehousing 15 continuously at the cathode, so that the metal layer 6 isformed in the solid electrolyte membrane 13.

The surface 4 a of the underlayer 4 contains oxide, and such surface 4 aof the underlayer 4 therefore presumably has higher activation energyfor the reduction reaction of the metal ions than the surface 5 a andthe side faces 5 b of the seed layer 5. With this configuration,although the solid electrolyte membrane 13 is in close contact with thesurface 5 a and the side faces 5 b of the seed layer 5 and the surface 4a of the underlayer 4, the current flows only at the surface 5 a and theside faces 5 b of the seed layer 5. Metal ions (copper ions in thiscase) contained in the solid electrolyte membrane 13 therefore arereduced on the surface 5 a and the side faces 5 b, and the metal (copperin this case) is deposited there. As a result, the metal layer 6 isselectively formed only on the surface 5 a and the side faces 5 b of theseed layer 5 of the surface 5 a and the side faces 5 b of the seed layer5 and the surface 4 a of the underlayer 4.

More specifically, as shown in FIG. 7, the rising potential of thepolarization curve (first polarization curve) of the material (forexample, WSi₂, ZrSi₂, ITO, and Ti) of the underlayer 4 is larger thanthe rising potential of the polarization curve (second polarizationcurve) of the material (in this case, silver) of the seed layer 5. Thismeans that the surface 4 a of the underlayer 4 has higher activationenergy for the reduction reaction of metal ions than the surface 5 a andthe side faces 5 b of the seed layer 5. The rising potential is thepotential at which the current density starts to rise. It is difficultto specify the rising potential when the current density is closer to 0mA/cm² (error will increase), so the potential corresponding to thecurrent density of 0.1 mA/cm² is used as the rising potential in thiscase. The rising potential of the polarization curve of WC issubstantially the same as the rising potential of the polarization curve(second polarization curve) of the material (in this case, silver) ofthe seed layer 5. WC therefore cannot be used as the underlayer 4. Thepolarization curves shown in FIG. 7 will be described later, withreference to Examples.

For example, a natural oxide film of SiO₂ is formed on the surface ofWSi₂ and ZrSi₂. The potential at a current density of 0.1 mA/cm² inthese polarization curves therefore is higher than the potential at acurrent density of 0.1 mA/cm² in the silver polarization curve by 0.02 Vor more. This means that voltage of, e.g., 0.1 V applied between theanode 11 made of copper and the underlayer 4 made of WSi₂ or ZrSi₂ flowscurrent through the seed layer 5 made of silver, and no current flowsthrough the underlayer 4 made of WSi₂ or ZrSi₂. In other words, whilecurrent flows through the seed layer 5, no current flows through theunderlayer 4 because the underlayer 4 includes oxide on the surface 4 aand the activation energy of the surface 4 a is relatively high asstated above. In this way, a difference in rising potential of thepolarization curve between the underlayer 4 and the seed layer 5 issufficiently large (about 0.02 V or more), and this allows selectiveformation of the metal layer 6 on the seed layer 5, i.e., only on thesurface 5 a and the side faces 5 b of the seed layer 5 of the surface 5a and the side faces 5 b of the seed layer 5 and the surface 4 a of theunderlayer 4 that are in close contact with the solid electrolytemembrane 13. In this way, the metal layer 6 is formed not only on thesurface 5 a of the seed layer 5 but also on the side faces 5 b, and thisimproves the adhesion between the metal layer 6 and the seed layer 5 ascompared with the case of the formation of the metal layer 6 only on thesurface 5 a of the seed layer 5.

When voltage is continuously applied between the anode 11 and theunderlayer 4 in this state, the metal layer 6 is gradually formed on thesurface 5 a and the side faces 5 b of the seed layer 5, and thethickness of the metal layer 6 increases. At this time, the metal layer6 on each of the side faces 5 b grows from the side face 5 b in thedirection along the surface 4 a of the underlayer 4 (left-rightdirection in FIG. 8), and the metal layer 6 is formed on the surface 4 aof the underlayer 4 only at a part close to the seed layer 5.

When metal (copper in this case) is deposited on the surface 5 a and theside faces 5 b of the seed layer 5, current concentrates on both ends ofthe surface 5 a of the seed layer 5 in FIG. 6. The metal layer 6therefore grows in the width direction as well so that the metal layer 6becomes wider in accordance with a distance from the seed layer 5. Whenthe thickness of the metal layer 6 increases from the state of FIG. 6,the solid electrolyte membrane 13 has a distance from the lower ends ofthe side faces 5 b of the seed layer 5 as shown in FIG. 8. The metallayer 6 therefore will not grow on the side faces 5 b of the seed layer5.

Continuously applied voltage between the anode 11 and the underlayer 4therefore results in the shape of the metal layer 6 as shown in FIG. 8.Specifically, thickness T1 of the metal layer 6 on the surface 5 a ofthe seed layer 5 is larger than thickness T2 of the metal layer 6 on theside face 5 b.

When the metal layer 6 is formed to have predetermined thickness T1,application of voltage between the anode 11 and the underlayer 4 isstopped, and pressurization of the metallic solution L by the pump 102is stopped. Then, the housing 15 is raised to a predetermined height,and the substrate 2 is removed from the metallic mount 40.

As stated above, the metal-layer formation step S3 forms the metal layer6 by electrolytic plating, and this increases the film-deposition rateand so shortens the plating time as compared with the case of formingthe metal layer 6 by electroless plating.

The removing step S4 removes the exposed region R without the seed layer5 and the metal layer 6 of the underlayer 4 without using a mask, sothat the wiring layer 3 including the underlayer 4 b, the seed layer 5and the metal layer 6 is formed on the surface of the substrate 2. Themethod for removing the exposed region R is not limited especially, andvarious methods, such as plasma etching, sputtering, and chemicaletching, may be used. In one example, when the underlayer 4 is made ofWSi₂ or ZrSi₂, the exposed region R is removed by plasma etching usingCF₄ gas in some embodiments.

The line/space of the wiring layer 3 is not particularly limited. In oneexample, when the space of the seed layer 5 is 2 μm, about 1 μm is keptfor the space of the wiring layer 3. From this point of view, when theline/space of the seed layer 5 is 2 μm or more and 100 μm or less/2 μmor more and 100 μm or less, for example, the line/space of the wiringlayer 3 will be 3 μm or more and 101 μm or less/1 μm or more and 99 μmor less. The wiring board 1 having such fine wiring is suitable forhigh-density mounting. The line/space is the wiring width W1/wiringspace W2 in a plan view of the wiring board 1 (see FIG. 9).

As shown in FIG. 9, the wiring layer 3 is formed in a taper shape(trapezoidal shape in FIG. 9) that tapers in accordance with a distancefrom the substrate 2 in a portion 3 a closer to the substrate 2 than thesurface 5 a of the seed layer 5. The wiring layer 3 is formed in areverse taper shape (reverse trapezoidal shape in FIG. 9) that becomesthicker in accordance with a distance from the substrate 2 in a portion3 b farther from the substrate 2 than the surface 5 a of the seed layer5. The width of the taper-shaped part (portion 3 a) of the metal layer 6is smaller than the width of the reverse taper-shaped part (portion 3 b)of the metal layer 6. This keeps the wiring width with the reversetaper-shaped part, and widens the wiring interval (wiring interval inthe vicinity of the surface of the substrate 2) between the taper-shapedparts. This therefore keeps insulation reliability between the wirings.

Thickness T1 of the metal layer 6 on the surface 5 a of the seed layer 5is larger than thickness T2 of the metal layer 6 on the side face 5 b.This keeps the thickness of the wiring layer 3 without narrowing thewiring interval of the wiring layer 3, and so easily keeps theinsulation reliability between the wirings. In one example, thickness T1of the metal layer 6 on the surface 5 a is 1 μm or more and 100 μm orless, and thickness T2 of the metal layer 6 on the side face 5 b is 2 μmor less. Thickness T1 of the metal layer 6 that is 1 μm or more avoidstoo large wiring resistance even when the wiring layer 3 is fine wiring.Thickness T1 of the metal layer 6 that is 100 μm or less avoids too longtime (plating time) required to form the metal layer 6.

In this way the method manufactures the wiring board 1 shown in FIG. 9.

In the present embodiment, the solid electrolyte membrane 13 is pressedagainst the seed layer 5 and the underlayer 4, and voltage is appliedbetween the anode 11 and the underlayer 4 as described above. Thisreduces metal ions contained in the solid electrolyte membrane 13 so asto form the metal layer 6 on the surface 5 a and the side faces 5 b ofthe seed layer 5. To form the metal layer 6 on the surface 5 a of theseed layer 5, the solid electrolyte membrane 13 is pressed against theseed layer 5 and the underlayer 4. At this time, the solid electrolytemembrane 13 comes into close contact with the underlayer 4 as well asthe seed layer 5. The surface 4 a of the underlayer 4 contains oxide,and such a surface 4 a of the underlayer 4 therefore presumably hashigher activation energy for the reduction reaction of the metal ionsthan the surface (surface 5 a and side faces 5 b) of the seed layer 5.This selectively forms the metal layer 6 only on the surface of the seedlayer 5 of the seed layer 5 and the underlayer 4, and so enables theformation of the metal layer 6 on the surface of the seed layer 5without using a resin resist pattern. The exposed region R of theunderlayer 4 without the seed layer 5 and the metal layer 6 is thenremoved, and this forms the wiring layer 3 having a predetermined wiringpattern on the surface of the substrate 2. As stated above, the methodforms the metal layer 6 on the surface of the seed layer 5 without usinga resin resist pattern, and so the method does not need the formationand removal of a resist pattern. As a result, the method does notrequire a lot of steps to manufacture the wiring board 1 and does notgenerate a large amount of liquid waste.

While the solid electrolyte membrane 13 is pressed against the seedlayer 5 and the underlayer 4, voltage is applied between the anode 11and the underlayer 4. This forms the metal layer 6 while deforming thesolid electrolyte membrane 13 so as to follow the shapes of the seedlayer 5 and the underlayer 4. As a result, the metal layer 6 is formedon the surface 5 a as well as the side faces 5 b of the seed layer 5, sothat the metal layer 6 is formed to cover the surface 5 a and the sidefaces 5 b of the seed layer 5. This improves the adhesion between themetal layer 6 and the seed layer 5 as compared with the case of theformation of the metal layer 6 only on the surface 5 a of the seed layer5.

EXAMPLES

The following describes Examples of the present disclosure.

<Material of Seed Layer>

Example 1

The wiring board 1 was manufactured by the above-described manufacturingmethod, using glass as the material of the substrate 2, WSi₂ as thematerial of the underlayer 4, silver as the material of the seed layer5, and copper as the material of the metal layer 6. Specifically, theunderlayer 4 made of WSi₂ was formed on the surface of a substrate 2made of glass by sputtering using WSi₂ as a target. At this time, thethickness of the underlayer 4 was 100 nm. Then, the seed layer 5 havingthe thickness of 100 nm was formed on the surface of the underlayer 4using ink containing silver nanoparticles having the average particlediameter of 50 nm. At this time, the ink was disposed on the surface ofthe underlayer 4 by screen printing, and the silver nanoparticles weresintered at the temperature of 120° C. to form the seed layer 5. Theseed layer 5 was formed to have a plurality of independent patterns 5 c.

Next, the metal layer 6 was formed on the surface 5 a of the seed layer5 by the film-deposition apparatus 100. 1.0 mol/L copper sulfate aqueoussolution was used as the metal solution L, oxygen-free copper wire wasused as the anode 11, and Nafion (registered trademark) (thickness ofabout 8 μm) was used as the solid electrolyte membrane 13. While thesolid electrolyte membrane 13 was pressed against the seed layer 5 with1.0 MPa by the pump 102, the metal layer 6 was formed at the currentdensity of 0.23 mA/cm² with an applied voltage of about 0.5 V (constantcurrent control of about 100 mA). Thickness T1 of the metal layer 6 was5 μm.

After that, the exposed region R of the underlayer 4 without the seedlayer 5 and the metal layer 6 was removed by vacuum plasma etching usingCF₄ gas. The wiring board 1 of Example 1 was obtained in this way.

Example 2

The material of the underlayer 4 was ZrSi₂. Otherwise, the manufacturingmethod was the same as in Example 1.

Example 3

The material of the underlayer 4 was ITO. Otherwise, the manufacturingmethod was the same as in Example 1.

Example 4

The material of the underlayer 4 was Ti. Otherwise, the manufacturingmethod was the same as in Example 1.

Comparative Example 1

The material of the underlayer 4 was WC. Otherwise, the manufacturingmethod was the same as in Example 1.

Then, the wiring layers 3 in Examples 1 to 4 and Comparative Example 1were observed. FIG. 10 shows the results.

As shown in FIG. 10, the wiring layers 3 in Examples 1 to 4 werefavorably formed. Specifically, copper (metal layer 6) was not formed inthe region without the seed layer 5 (exposed region R of the underlayer4), and was formed only on the seed layer 5. The copper (metal layer 6)was uniformly formed on the seed layer 5, and the seed layer 5, forexample, was not exposed. On the contrary, deposition of copper (metallayer 6) was found also in the region without the seed layer 5 (theregion on WC) in Comparative Example 1. This shows that the metal layer6 was selectively deposited in Examples 1 to 4, and the metal layer 6was not (or less) selectively deposited in Comparative Example 1.

To examine the cause, polarization curves (polarization characteristics)of WSi₂, ZrSi₂, ITO, Ti, WC and silver were examined. Specifically,copper sulfate solution having concentration of 1 mol/L at thetemperature of 25° C. was used as an electrolyte, oxygen-free copperwire was used as a counter electrode, and a saturated calomel electrode(HC-205C manufactured by DKK-TOA Co.) was used as a reference electrode.Then the polarization curves (polarization characteristics) weremeasured by setting the potential sweep rate at 10 mV/sec, and using apotentiostat (HZ-7000 manufactured by Hokuto Denko Co.) with WSi₂,ZrSi₂, ITO, Ti, WC or silver as the working electrode. At this time, abeaker was used as the electrolytic cell, the amount of electrolyte was1.0 L, and the agitation rate was 300 rpm. As a result, the polarizationcurves (polarization characteristics) of WSi₂, ZrSi₂, ITO, Ti, WC andsilver were as shown in FIG. 7.

As shown in FIG. 7, differences in the rising potential of WSi₂, ZrSi₂,ITO, Ti, and WC relative to the rising potential of silver were about0.25 V, about 0.25 V, about 0.18 V, about 0.02 V, and about 0 V,respectively. The rising potential in this case was the potential at thecurrent density of 0.1 mA/cm².

This shows that a material having a rising potential difference of about0.02 V or more relative to the material of the seed layer 5 (in thiscase, silver) when the current density is 0.1 mA/cm² may be used as thematerial of the underlayer 4, and this enables the formation of themetal layer 6 only on the seed layer 5 and not in the region without theseed layer 5 (exposed region R of the underlayer 4). Such an underlayer4 having a large rising potential difference relative to the seed layer5 increases the selectivity of deposition during the formation of themetal layer 6. This prevents the deposition of the metal layer 6 on theunderlayer 4 even when the metal layer 6 is formed with a larger currentdensity, and so shortens the time required to form the metal layer 6.

<Cross-Sectional Shape of Wiring Layer>

Example 5

The material of the substrate 2 was glass epoxy resin, and thickness T1of the metal layer 6 on the surface 5 a of the seed layer 5 was 10 μm.Otherwise, the manufacturing method was the same as in Example 1. Then,the cross section of the wiring layer 3 in Example 5 was observed.

Similarly to the schematic cross-sectional view of FIG. 9, the metallayer 6 of Example 5 had a shape to cover the surface 5 a and the sidefaces 5 b of the seed layer 5. Thickness T1 of the metal layer 6 on thesurface 5 a of the seed layer 5 was larger than thickness T2 of themetal layer 6 on the side face 5 b. Thickness T1 of the metal layer 6 onthe surface 5 a was 10 μm, and thickness T2 of the metal layer 6 on theside face 5 b was 2 μm or less.

The wiring layer 3 was formed in a taper shape (trapezoidal shape inFIG. 9) that tapered in accordance with a distance from the substrate 2in a portion 3 a closer to the substrate 2 than the surface 5 a of theseed layer 5. The wiring layer 3 was formed in a reverse taper shape(reverse trapezoidal shape in FIG. 9) that became thicker in accordancewith a distance from the substrate 2 in a portion 3 b farther from thesubstrate 2 than the surface 5 a of the seed layer 5. The width of thetaper-shaped part (portion 3 a) of the wiring layer 3 was smaller thanthe width of the reverse taper-shaped part (portion 3 b) of the wiringlayer 3.

<Optimum Thicknesses of Underlayer and Seed Layer>

Example 6

The thickness of the seed layer 5 was 300 nm. Otherwise, themanufacturing method was the same as in Example 1.

Example 7

The thickness of the seed layer 5 was 20 nm. Otherwise, themanufacturing method was the same as in Example 1.

Example 8

The thickness of the underlayer 4 was 300 nm. Otherwise, themanufacturing method was the same as in Example 1.

Example 9

The thickness of the underlayer 4 was 20 nm. Otherwise, themanufacturing method was the same as in Example 1.

Example 10

The thickness of the seed layer 5 was 10 nm. Otherwise, themanufacturing method was the same as in Example 1.

Example 11

The thickness of the underlayer 4 was 10 nm. Otherwise, themanufacturing method was the same as in Example 1.

In Examples 6, 7, and 10, the thickness of the seed layer 5 was adjustedby adjusting the coating amount of the ink. In Examples 8, 9, and 11,the thickness of the underlayer 4 was adjusted by adjusting thesputtering time. Then, the wiring layers 3 in Example 1, 6˜11 wereobserved. FIG. 11 shows the results.

As shown in FIG. 11, the wiring layers 3 in Examples 1, 6 to 9 werefavorably formed. Specifically, the copper (metal layer 6) was notformed in the region without the seed layer 5 (exposed region R of theunderlayer 4), and was formed only on the seed layer 5. The copper(metal layer 6) was uniformly formed on the seed layer 5, and the seedlayer 5, for example, was not exposed. It was therefore found that thewiring board 1 can be favorably formed by setting the thickness of theunderlayer 4 at 20 nm or more and 300 nm or less and the thickness ofthe seed layer 5 at 20 nm or more and 300 nm or less.

In Examples 10 and 11, copper (metal layer 6) was not formed in theregion without the seed layer 5 (exposed region R of the underlayer 4),and was formed only on the seed layer 5. However, the copper (metallayer 6) was not formed in a partial region on the seed layer 5, meaningthat unevenness occurred. The degree of unevenness occurred at a part ofthe copper (metal layer 6) as in Examples 10 and 11 does not pose aproblem of the wiring board 1 for use.

The wiring board 1 having a thickness of the underlayer 4 more than 300nm and a thickness of the seed layer 5 more than 300 nm can be stillfavorably formed. This, however, degrades the cost effectiveness becausethe material cost and the process cost required for forming theunderlayer 4 and the seed layer 5 and removing the underlayer 4increase.

Example 12

The material of the substrate 2 was glass epoxy resin, and thecenter-line average roughness Ra of the substrate 2 was 0.1 μm.Otherwise, the manufacturing method was the same as in Example 1.

Example 13

The center-line average roughness Ra of the substrate 2 was 0.5 μm.Otherwise, the manufacturing method was the same as in Example 12.

Example 14

The center-line average roughness Ra of the substrate 2 was 1.0 μm.Otherwise, the manufacturing method was the same as in Example 12.

Example 15

The center-line average roughness Ra of the substrate 2 was 1.2 μm.Otherwise, the manufacturing method was the same as in Example 12.

Comparative Example 2

The material of the substrate 2 was glass epoxy resin, and thecenter-line average roughness Ra of the substrate 2 was 0.1 μm. Then,copper wiring was formed on the surface of the substrate 2 byelectroless plating using a known semi-additive method.

Comparative Example 3

The center-line average roughness Ra of the substrate 2 was 0.5 μm.Otherwise, the manufacturing method was the same as in ComparativeExample 2.

Comparative Example 4

The center-line average roughness Ra of the substrate 2 was 1.0 μm.Otherwise, the manufacturing method was the same as in ComparativeExample 2.

Comparative Example 5

The center-line average roughness Ra of the substrate 2 was 1.2 μm.Otherwise, the manufacturing method was the same as in ComparativeExample 2.

The center line average roughness Ra of the substrate 2 in Examples 12to 15 and Comparative Examples 2 to 5 was adjusted during themanufacturing of the substrate 2. Then a peeling test was conducted toExamples 12 to 15 and Comparative Examples 2 to 5. The width of thewiring layer 3 was set at 10 mm, and the wiring layer 3 was pulled inthe direction perpendicular to the substrate 2.

As shown in FIG. 12, the adhesion of the wiring layer 3 to the substrate2 in Examples 12 to 15 was about 0.8 kN/m, about 0.87 kN/m, about 0.9kN/m, and about 0.85 kN/m, respectively. In all of Examples 12 to 15,breakage (peeling) occurred inside the substrate 2. In this way, it wasfound that the wiring layers 3 in Examples 12 to 15 were firmly bondedto the substrate 2 regardless of the center-line average roughness Ra oftheir substrates 2.

The adhesion of the wiring layer 3 to the substrate 2 in ComparativeExamples 2 to 5 was about 0.1 kN/m, about 0.4 kN/m, about 0.64 kN/m, andabout 0.89 kN/m, respectively. In Comparative Examples 2 to 4, peelingoccurred at the interface between the wiring layer 3 (copper wiring byelectroless plating) and the substrate 2, and breakage (peeling)occurred inside the substrate 2 only in Comparative Example 5. In thisway, it was found that, when the center-line average roughness Ra of thesubstrate 2 was 1.0 μm or less, Comparative Examples 2 to 5 had thedifficulty of firmly bonding the wiring layers 3 (copper wiring byelectroless plating) to the substrate 2. On the contrary, themanufacturing method of the present embodiment was able to firmly bondthe wiring layers 3 to the substrate 2 as shown in Examples 12 to 15,even when the center-line average roughness Ra of the substrate 2 was1.0 μm or less. The manufacturing method of the present embodiment istherefore particularly effective when the center-line average roughnessRa of the substrate 2 is 1.0 μm or less.

The adhesion of the wiring layer 3 to the substrate 2 in Examples 12 to15 was improved because these Examples formed the underlayer 4 on thesurface of the substrate 2 by sputtering, and this firmly bonded thesubstrate 2 and the underlayer 4 due to the covalent bond of Si—O.Similarly, the formation of the underlayer 4 on the surface of thesubstrate 2 by evaporation also firmly bonds the substrate 2 and theunderlayer 4 due to the covalent bond, and this also improves theadhesion of the wiring layer 3 to the substrate 2.

Example 16

The material of the underlayer 4 was ZrSi₂, and the thickness of theunderlayer 4 was 100 nm. Otherwise, the manufacturing method was thesame as in Example 1. Then, the wiring layer 3 in Example 16 wasobserved.

As shown in FIG. 13, the wiring layer 3 in Example 16 was favorablyformed. Specifically, copper (metal layer 6) was not formed in theregion without the seed layer 5 (exposed region R of the underlayer 4),and was formed only on the seed layer 5. The copper (metal layer 6) wasuniformly formed on the seed layer 5, and the seed layer 5, for example,was not exposed.

The embodiment disclosed here is to be considered in all respects asillustrative and not restrictive. The scope of the present disclosure isdefined by the claims and not by the embodiment, and is intended toinclude any modification within the meaning and scope equivalent to theterms of the claims.

For example, the above embodiment shows an example of having the wiringlayer 3 only on one surface of the substrate 2, and the presentdisclosure is not limited to this. In another example, a wiring layer 3may be provided on one surface and the other surface of the substrate 2(both of the upper and lower faces) to form a two-layered substrate. Inanother embodiment, the substrate may be a multilayer substrate havingfour layers (or four layers or more).

The above embodiment describes an example of the manufacturing method ofthe wiring board 1 including the underlayer formation step S1 and theseed-layer formation step S2. That is, the above embodiment describesthe example of including the step of forming the underlayer 4 on thesurface of the substrate 2 and the step of forming the seed layer 5 onthe surface of the underlayer 4. The present disclosure is not limitedto this, and the method may prepare the substrate 2 having theunderlayer 4 on the surface, and then form the seed layer 5 on thesurface of the underlayer 4, or may prepare the substrate 2 having thelamination of the underlayer 4 and the seed layer 5 on the surface andthen form the metal layer 6 on the surface of the seed layer 5.

All publications, patents and patent applications cited in the presentdescription are herein incorporated by reference as they are.

DESCRIPTION OF SYMBOLS

-   1 Wiring board-   2 Substrate-   3 Wiring layer-   3 a, 3 b Portion-   4, 4 b Underlayer-   4 a Surface-   5 Seed layer-   5 a Surface-   5 b Side face-   5 c Independent pattern-   6 Metal layer-   9 Substrate with seed-layer-   11 Anode-   13 Solid electrolyte membrane-   L Metallic solution-   R Exposed region-   T1, T2 Thickness

What is claimed is:
 1. A method for manufacturing a wiring boardincluding an insulating substrate, and a wiring layer with apredetermined wiring pattern disposed on the surface of the insulatingsubstrate, the method comprising: preparing a substrate with seed-layer,the substrate with seed-layer including: an electrically conductiveunderlayer on the surface of the insulating substrate; and a seed layerwith a predetermined pattern corresponding to the wiring pattern on thesurface of the underlayer, the seed layer containing metal; disposing asolid electrolyte membrane between an anode and the seed layer as acathode, pressing the solid electrolyte membrane against the seed layerand the underlayer, and applying voltage between the anode and theunderlayer to reduce metal ions contained in the solid electrolytemembrane and so form a metal layer on the surface of the seed layer; andremoving an exposed region of the underlayer without the seed layer andthe metal layer to form the wiring layer including the underlayer, theseed layer and the metal layer on the surface of the insulatingsubstrate, and so manufacture the wiring board, during formation of themetal layer on the surface of the seed layer, at least a region of thesurface of the underlayer, on which the seed layer is not formed,containing oxide.
 2. The method for manufacturing the wiring boardaccording to claim 1, wherein during formation of the metal layer on thesurface of the seed layer, a natural oxide film including the oxide isformed in at least a region of the surface of the underlayer, on whichthe seed layer is not formed.
 3. The method for manufacturing the wiringboard according to claim 1, wherein when copper sulfate solution withconcentration of 1 mol/L at a temperature of 25° C. is used as anelectrolyte, oxygen-free copper wire is used as a counter electrode, asaturated calomel electrode is used as a reference electrode, and afirst polarization curve using the material of the underlayer as aworking electrode and a second polarization curve using the metal of theseed layer as a working electrode are measured while setting a potentialsweep rate at 10 mV/sec, potential of the first polarization curve at acurrent density of 0.1 mA/cm2 is higher than potential of the secondpolarization curve at a current density of 0.1 mA/cm2 by 0.02 V or more.4. The method for manufacturing the wiring board according to claim 1,wherein when preparing the substrate with seed-layer, the methodprepares a substrate including a surface with center-line averageroughness Ra of 1 μm or less as the insulating substrate, and forms theunderlayer by sputtering on the surface of the insulating substrate. 5.The method for manufacturing the wiring board according to claim 4,wherein the seed layer is formed on the surface of the underlayer sothat line/space is 2 μm or more and 100 μm or less/2 μm or more and 100μm or less.
 6. The method for manufacturing the wiring board accordingto claim 1, wherein when preparing the substrate with seed-layer, themethod places ink containing metal nanoparticles on the surface of theunderlayer, and then sinters the metal nanoparticles to form the seedlayer.
 7. The method for manufacturing the wiring board according toclaim 1, wherein when preparing the substrate with seed-layer, themethod forms the seed layer on the surface of the underlayer so that thepredetermined pattern of the seed layer has a plurality of independentpatterns that are spaced away from each other.